Fibers treated with polymerization compounds and fiber reinforced composites made therefrom

ABSTRACT

Methods of making fiber reinforced composite articles are described. The methods may include treating fibers with a sizing composition that includes a polymerization compound, and introducing the treated fibers to a pre-polymerized composition. The combination of the treated fibers and pre-polymerized composition may then undergo a temperature adjustment to a polymerization temperature at which the pre-polymerized composition polymerizes into a plastic around the fibers to form the fiber-reinforced composite article. Techniques for introducing the treated fibers to the pre-polymerized composition may include pultrusion, filament winding, reactive injection molding (RIM), structural reactive injection molding (SRIM), resin transfer molding (RTM), vacuum-assisted resin transfer molding (VARTM), long fiber injection (LFI), sheet molding compound (SMC) molding, bulk molding compound (BMC) molding, a spray-up application, and/or a hand lay-up application, among other techniques.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of prior U.S. applicationSer. No. 12/881,736 filed Sep. 14, 2010, which is a continuation-in-partof prior U.S. application Ser. No. 12/724,024 filed Mar. 15, 2010, whichis a continuation-in-part of U.S. application Ser. No. 12/008,041 filedJan. 8, 2008. The entire contents of the above-identified applicationsare herein incorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

Fiber-reinforced composites are used in a variety of parts andequipment, including automotive parts, boat parts, building elements,and aircraft parts, among other types of articles. One well establishedmethod of making these articles is to place the bare fibers in a moldand then flow in the liquid precursors of a thermoset polymer. Once theprecursors have infused through the fibers and filled the mold, a curingstage ensues where the precursor polymerize into a thermoset polymermatrix surrounding the fibers. The fiber-reinforced composite may thenbe released from the mold and, if necessary, shaped, sanded, orotherwise processed into the final article.

Producing fiber-reinforced composites with widely available glass fibersand uncured thermoset resins is inexpensive and usually does not requirecomplex equipment or extreme processing conditions (e.g., hightemperatures) to produce the final articles. Still, there aresignificant disadvantages associated with making fiber-reinforcedthermoset articles, as well as deficiencies with the composites in manyapplications. One considerable disadvantage with making these articlesis the health and safety problems posed by working with uncuredthermoset resins. These resins often produce a lot of volatile organiccompounds (VOCs), many of which are irritants and even carcinogens.Outgasing VOCs are particularly problematic during curing processes whenexothermic polymerization reactions raise the temperature of thecomposite and increase rate which these compounds evaporate into thesurrounding atmosphere. In order to prevent VOC concentrations fromexceeding safe limits, expensive ventilation and air treatment equipmentis required. This equipment is particularly costly and difficult tomaintain for the manufacture of larger composite articles, such as boathulls and wind-turbine blades.

Another significant problem with making fiber-reinforced thermosetcomposites is the large amounts of unrecyclable waste they generate.Glass reinforced polyester and epoxy wastes do not easily decompose,making them expensive to landfill. When they are contaminated with toxicprecursors, such as epoxy prepregs, they present an even greaterenvironmental challenge. The inability to recycle most fiber-reinforcedthermosets also presents a disposal challenge when the articles madefrom these composites reach the end of their useful lives. The size ofthis challenge only increases with the size of the articles that must bediscarded.

Larger-sized articles present additional challenges for thermosetcomposites. Thermosets in general cannot be welded or melted, whichmakes it very difficult, if not impossible, to modify or repairthermoset parts once they have been cured. The high degree ofcrystallinity that is characteristic of many thermoset polymers alsomakes the composites prone to fractures that cannot easily be repaired.When fractures and other defects form in larger thermoset articles,often the only option is to replace the article at significant cost.

In view of the significant difficulties with both the manufacture andproperties of larger articles made from fiber-reinforced thermosetcomposites, alternative materials are being investigated. One areareceiving interest in replacing or blending the thermoset polymers withthermoplastic polymers. Thermoplastics have advantages over thermosetsin many article applications, including a usually superior fracturetoughness and chemical resistance that can increase the damage toleranceand useable lifetimes in larger articles. The increased toughness offiber-reinforced thermoplastic composites often means less material isneeded to make an article.

Starting monomers for many thermoplastics are less toxic than those ofwidely used thermosets, and they produce significantly less noxiousgases during article production. Many thermoplastics are also meltableand weldable, which allows larger parts to be repaired instead ofprematurely replaced. Thermoplastics are generally also recyclable,which significantly decreases environmental impact and waste disposalcosts both during manufacturing as well as at the end of an article'slifecycle.

Unfortunately, thermoplastics also have production challenges includingsignificantly higher flow viscosities than uncured thermoset resins. Theflow viscosities of widely used thermoplastic polymers may be orders ofmagnitude higher than uncured epoxy, polyester, and vinylester thermosetresins, which have flow viscosities comparable to water. The higher flowviscosities makes it difficult for thermoplastic resins to infiltrate afiber mat and produce a homogeneous polymer matrix composite that isfree of voids and seams. Oftentimes, it is necessary to introduce thethermoplastic resin under high temperature or high vacuum, whichincreases the costs and complexity of manufacturing processes. Thus,there is a need for new methods and materials to make fiber-reinforcedplastic composites with reduced production problems and improved bondingbetween the fibers and the polymer matrix. These and other issues areaddressed in the present application.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention include methods of making fiber reinforcedcomposite articles. The methods may include treating fibers with asizing composition that includes a polymerization compound, andintroducing the treated fibers to a pre-polymerized composition. Thecombination of the treated fibers and pre-polymerized composition maythen undergo a temperature adjustment (e.g., heating) to apolymerization temperature at which the pre-polymerized compositionpolymerizes into a plastic around the fibers to form thefiber-reinforced composite article. Techniques for introducing thetreated fibers to the pre-polymerized composition may includepultrusion, filament winding, reactive injection molding (RIM),structural reactive injection molding (SRIM), resin transfer molding(RTM), vacuum-assisted resin transfer molding (VARTM), long fiberinjection (LFI), sheet molding compound (SMC) molding, bulk moldingcompound (BMC) molding, a spray-up application, and/or a hand lay-upapplication, among other techniques.

Embodiments of the invention further include additional methods ofmaking a fiber-reinforced composite article. The methods may includeproviding fibers to an article template, where the fibers have beentreated with a sizing composition that includes a polymerizationcompound, such as an uncoupled initiator compound, a coupling-initiatorcompound and/or a catalyst, among other compounds. The methods mayfurther include providing a pre-polymerized mixture to the articletemplate, where the pre-polymerized mixture may include a monomer, andoptionally a catalyst. The combination of the fibers and thepre-polymerized mixture may be heated to a polymerization temperaturewhere the monomers polymerize around the fibers and form at least aportion of the composite article. The article may then be removed fromthe article template.

Embodiments of the invention still further include additional methods ofmaking a fiber-reinforced composite article. The methods may includeproviding a pre-polymerized fiber-containing material comprising fibersin contact with a combination of a monomer, and optionally apolymerization catalyst, where the fibers have been treated with apolymerization compound. The method may also include applying thepre-polymerized fiber-containing material to an article template, andheating the pre-polymerized fiber-containing material to apolymerization temperature. The monomers polymerize around the fibers toform at least a portion of the composite article.

Embodiments of the invention may include one or more treated fibers thatpromote a polymerization reaction to form a fiber-reinforced compositearticle. The treated fiber may have at least one treated surface thatincludes a polymerization compound. The polymerization compound mayinitiate or catalyze the polymerization of a pre-polymerized compositionto form a plastic matrix of the fiber-reinforced composite article.

Embodiments of the invention also include fiber-reinforced compositearticles. The articles may include a plastic polymer matrix and fiberscoupled to the matrix by a reacted polymerization compound that wasprovided with the fibers through treatment with a sizing compositionprior to the fibers being introduced to the pre-polymerized compositionthat polymerizes into the plastic polymer matrix. The polymerizationcompound may initiate the polymerization of a pre-polymerizedcomposition to form the plastic polymer. Examples of thefiber-reinforced composite articles may include wind turbine blades forelectric power generation, among other articles.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components. In someinstances, a sublabel is associated with a reference numeral and followsa hyphen to denote one of multiple similar components. When reference ismade to a reference numeral without specification to an existingsublabel, it is intended to refer to all such multiple similarcomponents.

FIG. 1A shows a flowchart with selected steps in methods of makingfiber-reinforced composite articles according to embodiments of theinvention;

FIG. 1B shows a flowchart with selected steps in additional methods ofmaking fiber-reinforced composite articles according to embodiments ofthe invention;

FIG. 2 shows a flowchart with selected steps in additional methods ofmaking fiber-reinforced composite articles according to embodiments ofthe invention;

FIG. 3 illustrates a simplified cross-sectional drawing of an articletemplate for making a wind turbine blade according to embodiments of theinvention; and

FIG. 4 illustrates a simplified cross-sectional drawing of an articletemplate for a one-shot method of making a wind turbine blade accordingto embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Articles made from fiber-reinforced plastic polymer composites aredescribed, as well as methods of making these articles. These articlesinclude, without limitation, equipment and parts for varioustransportation vehicles such as cars, trucks, boats, aircraft, trains,and non-motorized vehicles such as bicycles and sailboats, among otherkinds of transportation vehicles. The articles may further includeequipment and parts used in industrial applications, including parts forelectric power generation, such as wind turbine blades.

The present composite materials may be used to make large-sized articlesthat were previously made from a greater number of smaller pieces whichwere coupled together to make the larger article. The ability of thecomposites to make the article from a smaller number of pieces, or evena single piece, reduces manufacturing complexity as well as the numberof joints, fasteners, and seams that can weaken the overall structuralintegrity of the article. An exemplary longest dimension for a 1 argearticle may be about 1 meter or more, about 5 meters or more, about 10meters or more, about 15 meters or more, about 20 meters or more, about25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100meters or more, among other ranges of a longest dimension.

The present methods permit the formation of fiber-reinforced compositearticles of larger sizes, increased fracture toughness and corrosionresistance, and longer operational lifetimes. These methods include theuse of fibers treated with a sizing composition that contains one ormore polymerization compounds that initiate and/or catalyze thepolymerization of a pre-polymerized composition to form a polymer matrixof the composite. Polymerization compounds may include catalysts, anduncoupled initiators compounds that are not covalently bonded to asurface of the fiber. They may also include coupling-initiator compoundsthat have a coupling moiety designed to react with and bond to thefiber, and a more distal positioned initiator moiety that can cause thepolymerization of a pre-polymerized composition surrounding the fibers.Exemplary sizing compositions may include combinations of uncoupledpolymerization initiators, polymer catalysts, and/or coupling-initiatorcompounds.

The ratio of uncoupled initiators to coupling-initiator compounds may beadjusted to balance the strength and fracture toughness (i.e., impactresistance) of the final fiber-reinforced composite article. In manyinstances, strong covalent bonding between the fibers and surroundingplastic matrix created by coupling-initiator compounds enhance theoverall strength of the composite article. However, too much of thisbonding can reduce the fracture toughness of the article, creating atrade-off between strength and fracture toughness. By introducing acombination of uncoupled initiator compounds and coupling-initiatorcompounds in the sizing composition, the degree of strong covalentbonding between the fibers and surrounding plastic matrix may becontrolled to strike the desired balance between strength and fracturetoughness in the composite article.

The plastic matrix of the composite articles may be made fromthermosets, thermoplastics, or a combination of both. When the matrixincludes one or more thermoplastics, embodiments of the present methodscan address problems of high flow viscosity melted thermoplastics thatcomplicate the formation of the final composite article. Theseembodiments may include forming the polymer matrix in situ in an articlemold, instead of forming and melting the polymers before incorporating(e.g., injecting) them into the mold. This allows the lower viscositymonomers to be incorporated into the mold and infused around the fibersat lower temperatures, in shorter times, and with fewer voids and otherdefects caused by a slow flowing melted polymer.

The combinations of the pre-polymerized composition and polymerizationcompound may be selected to have a controllable difference between themelting temperature of the pre-polymerized composition and itspolymerization temperature. For example, the melting temperature of thecomposition may be lower by about 10° C. or more than its polymerizationtemperature. This permits the composition to be melted and incorporatedinto an article mold for a controlled period of time before increasingthe monomer to its polymerization temperature to perform in situpolymerization. It also permits variable control of the timing of thepolymerization stage instead of having to work within a fixed,predetermined time of polymerization. For example, inspections andquality checks may be performed to insure the pre-polymerizedcomposition is homogeneously distributed in the mold before thetemperature is raised to the polymerization temperature. In contrast,many conventional methods require fixed polymerization times that cannotbe significantly accelerated or delayed.

The pre-polymerized composition may be liquid or solid at roomtemperature. When the pre-polymerized mixture is a solid, it may beintroduced to the mold or treated fibers as a solid (e.g., particles,fiber prepreg, etc.) before raising the temperature to between themelting and polymerization temperature. This allows the pre-polymerizedcomposition to melt and infuse around the fibers, and conform to theshape of the mold when a mold is used, before being polymerized.Examples may further include adding combinations solid and liquidpre-polymerized composition to the treated fibers prior to and/or duringpolymerization.

Exemplary Methods

FIG. 1A shows selected steps in an exemplary method 100 of making afiber-reinforced composite article according to embodiments of theinvention. The method 100 may include the step of treating fibers with asizing composition that includes at least one polymerization compound102. The method may further include introducing together apre-polymerization composition and the treated fibers 104. Techniquesfor introducing the composition and fibers may include pultrusion,filament winding, reactive injection molding (RIM), structural reactiveinjection molding (SRIM), resin transfer molding (RTM), vacuum-assistedresin transfer molding (VARTM), long fiber injection (LFI), sheetmolding compound (SMC) molding, bulk molding compound (BMC) molding, aspray-up application, and/or a hand lay-up application, among othertechniques.

The method 100 may further include the step of adjusting the temperatureof the combination of the treated fibers and pre-polymerized compositionto a polymerization temperature at which the pre-polymerized compositionpolymerizes into a plastic matrix around the fibers to help form thefiber-reinforced composite article 106. After the polymerizingcombination is held at the polymerization temperature for set period oftime, the temperature may be adjusted again to allow the article to cooland set. When the composition is added in the liquid phase, it has atemperature at or above the melting point of the precursors and othercomponents, but below a temperature where significant polymerizationoccurs.

In addition to the polymerization compound, the sizing composition mayfurther include one or more solvents (e.g., water), film forming agents,lubricants, and/or silanes, among other components. The lubricants helpprotect the surface of the fibers from scratches and abrasions commonlycaused by fiber-to-fiber contact and friction during processing. Thesilanes may act as chemical linking agents by bonding to both the glassfiber and the plastic matrix. Silanes containing organosilane groups maybe coupling agents for glass fibers and organic polymers, and serve tobond the two materials in the composite article. Film formers canprovide a desired degree of bonding between the fibers in the fiberstrands to avoid fuzzing and excess filamentation during processing infiber manufacturing operations and/or fiber composite fabricationoperations. The sizing composition may be applied to the fibers byspraying and/or mixing, followed by drying to form the treated fibers.

The pre-polymerized composition that forms the plastic matrix mayinclude polymerizable precursors of thermoplastics such as polybutyleneterephthlalate (PBT), polyethylene terephthalate (PET), polyamide-6(PA-6), polyamide-12 (PA-12), polyamide-6,6 (PA-6,6), cyclicpoly(1,4-butylene terephthalate) (CBT), polyurethanes (TPU),polymethylmethacrylate (PMMA), polycarbonates (PC),polyphenylenesulphide (PPS), polyethylenenapthalate (PEN),polybutylenenaphthalate (PBN), polyether etherketone (PEEK), andpolyetherketoneketone (PEKK), and combinations of two or more of thesepolymers, among other polymers.

One exemplary pre-polymerized composition includes lactam monomers thatproduce polyamide (also called nylon) when polymerized. The lactammonomers may have the formula:

where R represents a C₃ to C₁₂ substituted or unsubstituted cyclichydrocarbon chain. The polymerization of these lactam monomers involvesthe opening of the cyclic hydrocarbon chain to make a linear chain withreactive carbonyl and amine groups separated by a —(CH₂)_(n)—hydrocarbon group.

One exemplary lactam monomer that enjoys wide commercial use iscaprolactam, which polymerizes into nylon 6. Other lactam monomers mayinclude butyrolactam (also known as 2-pyrrolidone) which polymerizesinto nylon 4; valerolactam which polymerizes into nylon 5; capryllactamwhich polymerizes into nylon 8; and lauryllactam which polymerizes intonylon 12; among other lacatams.

Another exemplary pre-polymerized composition includes one or moremacrocyclic polyester oligomers, that polymerize form a polyesterthermoplastic. Examples of these macrocyclic polyester oligomers includepolybutylene terephthalates, such as cyclic poly(1,4-butyleneterephthalate).

The polymerization compound, or compounds, may include polymerizationcatalysts, polymerization activators, uncoupled polymerization initiatorcompounds, and/or coupling-initiator compounds, among other compounds.The uncoupled polymerization initiator compounds may include aninitiator compound having a formula:

R—X—(I)_(n)

wherein n is an integer with a value of 1 to 5;

R comprises a terminal moiety selected from the group consisting of ahydrogen and a hydrocarbyl group;

X comprises a linking moiety that links the R moiety with the one ormore I moieties; and

(I)_(n) comprises one or more polymerization initiator moieties, whereineach of the initiator moieties is capable of initiating a polymerizationof the pre-polymerized composition, and wherein each of the initiatormoieties is the same or different.

Examples of the terminal moiety (R) may include a hydrogen atom, ahydrocarbon moiety such as CH₃—, C_(n)H_(2n+1)— where n is an integerfrom 2 to 20, an aromatic group such as a phenyl group, or an aminegroup, among other terminal moieties.

Examples of the linking moiety (X) may include a covalent bond, an alkylgroup, an aryl group, an alkene group, or an amine group, among otherlinking moieties.

When the pre-polymerized composition is a lactam precursor of apolyamide, the polymerization initiator moieties may have the formula:

where the carbonyl group is bonded to a linking moiety of the initiatorcompound and R represents a C₃ to C₁₂ substituted or unsubstitutedcyclic hydrocarbon chain. When the combination of the pre-polymer lactammixture and fibers is raised to the polymerization temperature, the ringstructure may open or be otherwise activated to initiate a branched orunbranched polymerized chain from the initiator moiety. For example, theinitiator moiety may have the formula:

In additional examples, the initiator compound may be formed from two ormore initiator precursors that react in situ to form the initiatorcompound. For example, one of the initiator precursors may be apolymerization compound in the sizing composition, while a secondinitiator precursor may be included in the pre-polymerized compositionthat is introduced to the treated fibers having the first initiatorcompound. When the treated fibers and pre-polymerized composition areintroduced, the first and second initiator precursors may react to formthe initiator compound capable of initiating the polymerization of thepolymerizable precursors in the pre-polymerized composition into theplastic around the fibers.

A specific example of a multi-part initiator system includes ethylbenzoate acting as a first initiator precursor polymerization compoundin the sizing composition used to treat the fibers, and sodiumcaprolactam acting as a second initiator precursor included in thepre-polymerized composition with lactam polymerizable precursors and acatalyst. When the treated fibers are introduced to the pre-polymerizedcomposition, the ethyl benzoate reacts with the sodium caprolactamaround the fibers to form the initiator.

Exemplary polymerization compounds may include catalysts. For example,when the pre-polymerized composition includes polymerizable lactamcompounds, the catalysts may include cationic catalysts, anioniccatalysts, and/or water. In cationic polymerizations, the catalyst maybe an acid that protonates the carbonyl oxygen and/or nitrogen group onthe lactam to start a nuclephilic reaction between the protonatedmonomer and a second lactam monomer. This reaction may be followed by aseries of ring-opening acylations of the primary amine to build thepolyamide chain.

In anionic polymerizations, the catalyst may include a base such as analkali metal, alkali-earth metal hydroxide, or alkali metal amide (amongother bases) that deprotonates the lactam nitrogen to form an anion thatreacts with a second lactam monomer. Subsequent proton transfer andpropagation reactions build the polyamide chain. In some instances, thereaction between the initial anion and the second lactam monomer may befurther facilitated by an activator compound, such as an acyl halide oranhydride (among other activators).

In hydrolytic polymerizations that involve water, polymerization may beinitiated when the water initiates a hydrolysis reaction that opens thelactam ring to form an amino acid. The amine group of the amino acidthen reacts with additional lactam monomers in subsequent ring-openingreactions to build the polyamide chain.

When the pre-polymerized compound includes macrocyclic polyesteroligomers, exemplary catalysts may include tin-containing compoundsand/or titanium-containing compounds. For example the catalysts mayinclude organotin and/or organotitanate compounds. Tin-containingcompounds may include monoalkyltin(IV) hydroxide oxides,monoalkyltin(IV) chloride dihydroxides, dialkyltin(IV) oxides,bistrialkyltin(IV) oxides, monoalkyltin(V) tris-alkoxides,dialkyltin(IV) dialkoxides, and trialkyltin(IV) alkoxides, among othertin-containing compounds. Exemplary titanium-containing compoundsinclude titanate tetraalkoxide compounds (e.g., tetraisopropyl titanate)and tetraalkyl titanate compounds (e.g., tetra(2-ethylhexyl)titanate),among others.

Exemplary polymerization compounds may include coupling-initiatorcompounds. Specific coupling-initiator compounds may be selected basedon the type of fiber and plastic used in the composite. Generallyspeaking, the coupling-initiator compounds may have the formulaC—X-(1)_(n), where C represents the coupling moiety, (I), represents npolymerization initiator moieties, and X represents a linking moietythat links the C moiety to the one or more I moieties. When the fibersare glass fibers, the coupling moiety C may include one or more silicongroups, and the coupling-initiator compound may be represented by theformula S—X—(I)_(n), where S represents a silicon-containing couplingmoiety and X and (I), have the same meaning as described above.

The fibers may be made from a material that can be treated with thesizing composition that includes the polymerization compound. Examplesof fibers include glass fibers (e.g., E-glass, etc.), ceramic fibers(e.g., aluminum oxide, silicon carbide, silicon nitride, siliconcarbide, basalt, etc.), carbon fibers (e.g., graphite, semi-crystallinecarbon, carbon nanotubes, etc.), metal fibers (e.g., aluminum, steel,tungsten, etc.), and polymer fibers (e.g., aramid, etc.). The fibers maybe arranged as a mono-axial and/or multi-axial, woven and/or non-wovenmat. In addition, the fibers may also include chopped and/or unchopped(i.e., continuous fibers). The mats may have multiple sections withdifferent weave styles, as well as combinations of woven and non-wovensections. In addition, the mats may have regions where chopped fibersare incorporated, for example to allow better wet out and resinpenetration in a preselected part or parts of the composite article.

FIG. 1B shows selected steps in an exemplary method 150 of making afiber-reinforced composite article according to embodiments of theinvention. The method 150 may include the step of providing fibers to anarticle template 152. The fibers are treated with a sizing compositionthat includes one or more polymerization compounds that facilitate thepolymerization of a pre-polymerized composition that forms a plasticmatrix in the composite article. These polymerization compounds mayinclude, a catalyst, an activator, a polymerization initiator, and/or acoupling-initiator compound.

The method 150 may further comprise providing a pre-polymerizedcomposition to the article template 154. The pre-polymerized compositionmay include precursor monomers and/or oligomers of the plastic,polymerization catalysts, and/or polymerization initiators, among othercomponents. The pre-polymerized composition may include partiallypolymerized compounds such as dimers, trimers, and/or oligomers of theplastic. The pre-polymerized composition may be added in the liquidphase to the article template, or added in the solid phase. When thecomposition is added in the liquid phase, it has a temperature at orabove the melting point of the precursors and other components, butbelow a temperature where significant polymerization occurs. When thecomposition is added in the solid phase, it may be added as particles tothe article template and/or exist as a pre-impregnated (“pre-preg”)coating on the fibers that are added to the template. Embodimentsfurther include providing the pre-polymerized composition as both aliquid-phase mixture and solid-phase mixture to the article template.

In liquid-phase additions, the polymer precursors and thecatalyst/initiator components may be kept separate until they areprovided to the article template. For example, a catalyst may becombined with the liquid-phase monomer immediately before or duringthere introduction (e.g., injection) into the article template.Alternatively, a monomer and catalyst may be combined and stored as asolid or liquid pre-polymerized mixture well before their introductionto the article template. While the liquid and solid phase mixtures ofthe pre-polymerized composition may exhibit some degree ofpolymerization—for example the formation of dimers, trimers, and/orother oligomers—they are still considered pre-polymerized sincesubstantially complete polymerization has not occurred. Similarly,pre-preg fibers that have a coating of B-stage thermoplastic materialssurrounding the fibers may still be considered a pre-polymerized mixtureor a component of the pre-polymerized mixture. For purposes of thisapplication, discussions of the polymerization of pre-polymerizedcompositions include polymerizations of dimers, trimers, and/or otheroligomers, as well as monomers of the polymer.

After the pre-polymerized composition is provided to the articletemplate and has made sufficient contact with the fibers, thecombination of composition and fibers may be heated to a temperaturewhere significant polymerization occurs, as shown in step 156. Forexample where the pre-polymerized composition includes caprolactam, thetemperature of the pre-polymerized mixture may be raised from a meltingtemperature of between about 80° C. and 120° C., to a polymerizationtemperature of about 120° C. or more (e.g., about 120° C. to about 220°C.). In additional examples, the pre-polymerized composition may have amelting temperature of about 80° C. to about 200° C. (e.g., about 100°C. to about 160° C.), and may have a polymerization temperature of about120° C. to about 220° C. (e.g., about 180° C. to about 220° C.).

At the polymerization temperature, the polymerization-initiator moietiesfacilitate polymerization around the fibers. As described above, in thecase of caprolactam the initiator moieties may have the formula:

where the carbonyl group is bonded to a linking moiety of thecoupling-initiator compound and R represents a C₃ to C₁₂ substituted orunsubstituted cyclic hydrocarbon chain. When the combination of thecaprolactam-containing, pre-polymerized composition and treated fibersis raised to the polymerization temperature, the ring structure may openor be otherwise activated to initiate a branched or unbranchedpolymerized chain from the initiator moiety.

At least a portion of the plastic matrix is formed by the polymerizationof the caprolactam monomers around the treated fibers. The initiatormoieties may start the formation of straight and/or branched polyamidepolymers whose formation is also aided by the one or more catalystssupplied by the treated fibers, the pre-polymerized composition, orboth. When coupling-initiator compounds are included in the treatedfibers, they create a covalently-bonded link between the surface of thefibers and the surrounding polymers that is significantly stronger thana bond formed by simply curing a polyamide resin in the presence ofuntreated fibers.

The plastic matrices may also include polymers that are not directlybonded to the treated fibers. These polymers may have been formed, forexample, through polymerizations that were not initiated at an initiatormoiety, and polymers that have fragmented or decoupled afterpolymerization was initiated at the moiety. Although these polymers maynot be directly bonded to the fibers, their columbic and physicalinteractions with the directly bonded polymers may further strengthenthe bonding between the treated fibers and the surrounding polymermatrix.

As the polymerization of the polymer precursors around the fibersprogress, a fiber-reinforced composite is formed in the articletemplate. The composite material may form a portion or whole of thecomposite article 158. The shape of the composite article may bedefined, at least in part, by the shape of the article template, whichacts as a mold. For example, the article template may be shaped suchthat the composite forms the front or back halves of a wind turbineblade that are joined in subsequent production steps. Alternatively, thearticle template may be designed for a one-shot fabrication of thecomposite article (e.g., forming both halves of the blade from a singlearticle template).

When the composite material has had sufficient time to solidify, it maybe removed from the article template 160. In some instances, removal maybe facilitated by applying release agents to the surfaces of the articletemplate that are exposed to the fibers and pre-polymerized compositionthat form the composite article. These release agents hinder the fibersand polymerizing precursors from binding with the template as thecomposite is formed.

The composite material may be removed from the template either before orafter the plastic matrix has fully formed. In instances where thecomposite material is removed before curing is completed, the curing hasprogressed to the point where the article is sufficiently solid toretain the shape of the article after removal from the template. Theremoved article may undergo subsequent processing steps, such assanding, cutting, polishing, washing, drilling, coating, and/orpainting, among other post-formation steps. In the case where thecomposite is a portion of an article, the removed article may undergosteps to form the whole article, such as gluing, gap filling, and/orfastening the composite to other components to make the whole article.

Referring now to FIG. 2, a flowchart outlines selected steps inadditional methods of making fiber-reinforced composites according toembodiments of the invention. The methods 200 may include providing apre-polymerized fiber containing material (e.g., a pre-preg), where thefibers are in contact with a combination of the polymer precursors(e.g., monomers, oligomers) and a polymerization catalyst 202. Examplesof the pre-polymerized fiber may include glass fibers that have beenpre-treated with a sizing composition that includes at least onepolymerization compound and coated with a pre-polymerized compositionthat includes polymer precursors, and optionally polymerizationcatalyst. The pre-polymerized composition may be applied above a meltingtemperature for the polymer precursors, but below a temperature wheresignificant polymerization occurs. Following the application of thepre-polymerized composition, the treated fibers may be cooled tosolidify the coating and stored until use.

That use may include applying the pre-polymerized fiber-containingmaterial to an article template 204 that may act as a mold for acomposite article. The pre-polymerized fiber-containing material may beapplied as a lay-up of fiber materials in the article template. In someembodiments the fibers may be arranged in a fiber mat before beingapplied to the template, or arranged to have a particular orientation orset of orientations during and/or after being layed-up in the template.

The methods 200 may optionally include applying additional layers offiber-containing material to the article template. These additionallayers may consist of untreated fibers, fibers treated with additionalpolymerization compounds, and additional layers of pre-polymerizedfiber-containing material. The fiber layers may be stacked on top ofeach other, and/or may be applied side-by-side in the article template.Embodiments may include positioning the pre-polymerized fiber-containingmaterial in specific locations of the article template to enhance thestrength and mass of the composite material in those areas. For example,one or more layers (or sections of layers) of the pre-polymerizedfiber-containing material may be positioned where the outer shell (i.e.,skin) of wind turbine blade makes contact with an internal supportstructure of the blade such as a rib and/or spar.

The methods 200 may also optionally include providing the same ordifferent pre-polymerized composition to the article template followingthe lay-up of the fiber-containing materials. The pre-polymerizedcomposition may include the same or different make up of polymerprecursors and/or catalysts, and may be provided to the fiber materialsin the article template by, for example, resin transfer molding (RTM),vacuum-assisted resin transfer molding (VARTM), among other techniques.

After the pre-polymerized fiber-containing material (and any additionalmaterials) have been applied to the article template, the materials maybe heated to a temperature where the pre-polymerized compositionpolymerizes to form a composite material 206. The polymerizationprocesses may include the activation of an initiator moiety on initiatorand/or coupling-initiator compounds present in the treated fiber. Thesemoieties start the formation of polymers (e.g., polyamide polymers) thatsurround the fibers of fiber composite. This composite may form either aportion or whole of a fiber-reinforced composite article.

In some embodiments, the article template (or a portion thereof) maybecome part of the composite article. In these embodiments, thefiber-reinforced composite is bonded to one or more surfaces of thearticle template that were exposed to the pre-polymerizedfiber-containing material. The composite article that is formed includesan outer layer made from the article template. In additionalembodiments, the fiber-reinforced composite may optionally be removedfrom the article template 208, and the template may be discarded orprepared for forming another composite article.

Exemplary Methods of Making a Wind Turbine Blade

Exemplary methods of making a wind turbine blade will now be describedwith reference to the article templates shown in FIGS. 3 and 4respectively. FIG. 3 shows an article template 302 for part of the outerskin of a wind turbine blade made from a fiber reinforced composite. Thetemplate 302 may be for the side of the blade which faces the windduring operation of the turbine. A second article template (not shown)is used to form the opposite side of the blade. The two skins may thenbe joined using fasteners, adhesives, gap fillers, etc. to form theouter surface of the blade. Internal blade components, such as spars andribs, may also be added when the skins are joined together.

The article template 302 may be made from a rigid material that has aninner surface 306 defining the shape of the outer skin. This surface maybe made from a material or treated (e.g., coated) to form a exposedlayer of material that facilitates the release of the fiber-reinforcedcomposite outer skin from the article template 302.

The article template 302 may further comprise a vacuum bag 308 that maybe fluid-tightly sealed to the peripheral edges of the template.Together, the liner of the vacuum bag 308 and inner surface 306 definean enclosed volume where the materials for the composite may be combinedand heated to form the fiber-reinforced composite outer skin.

The article template 302 may further include openings 310 and 312,through which pre-polymerized compositions may flow to make contact withthe fiber materials shown in fiber layer 314. As noted above, additionalpre-polymerized materials (e.g., solid pre-preg materials) may also bepresent with the fibers in the fiber layer 314.

When the vacuum bag 308 is evacuated, the change in air pressure betweenthe inside and outside of the vacuum bag 308 may press the bag lineragainst the fiber layer 314. In addition, a pressure differential causesthe pre-polymerized composition to flow through openings 310 and 312 toinfiltrate the fiber layer 314. In the embodiment shown, the flowingcomposition may form two fluid fronts at the forward and rear ends ofthe outer skin which may converge proximate to the middle of the skin.Additional flow configurations are possible depending upon the numberand positioning of the openings in the article template.

When the pre-polymerized composition has been distributed over the fiberlayer 314, the materials may be heated to a polymerization temperatureto start the formation of the fiber-reinforced composite. The heatingmay, for example, be carried out by a heating element 316 positionedproximate to the inner surface 306 of the article template 302. When thepolymerization process is sufficiently advanced, the nascent compositemay be allowed to cool at a pre-defined rate to ensure the outer skin isformed with the requisite mechanical properties. The outer skin may thenbe removed from the article template 302 so that it can be combined withthe other parts of the blade. The article template may be treated (e.g.,cleaned and prepared) to form another outer skin.

The article template 302 shown in FIG. 3 forms only a part of the outerskin of a wind turbine blade. FIG. 4 shows an article template 402 thatis designed to form a more complete outer skin for a wind turbine bladewith a one-shot manufacturing technique. The article template 402includes a first mold component 404 and a second mold component 406which are combined to form the one-shot article template 402. The firstand second mold components may have peripheral edges 408, 410 that canbe joined to form an air-tight seal.

One-shot methods of making a wind turbine blade with article template402 may include laying-up fiber materials in the first mold component404 to form a first fiber layer 412 in the component. Additionalmaterials such as particles of polymer precursors, initiators, and/orcatalysts, may also be added to the mold component 404 and/or fiberlayer 412. First and second internal support sections 414, 416 may beplaced in the first mold component 404 over the first fiber layer 412.The first and second internal support sections 414, 416 may be made fromrigid materials such as wood, ceramic, light-weight metal or alloy,and/or polymers, among other materials. The rigid material may besurrounded by a more flexible material (e.g., foam rubber) and aflexible membrane that may make contact with the fiber layers in thetemplate 402.

An additional fiber layer 418 may support a gap between the first andsecond support sections 414, 416. This fiber layer 418 may be convertedinto an internal support of the final composite that joins oppositesides of the blade for increased strength and stability. In additionalembodiments, two or more internal supports (or conversely no supports)may be formed in blade.

Another additional fiber layer 420 may be layed-up over the first andsecond support structures 414, 416 such that the ends of the fiber layer420 overlap or otherwise contact the complementary ends of first fiberlayer 412. The second mold component 406 may then be placed over thefiber layers and internal supports and secured to first mold component404 along the peripheral edges 408, 410.

Openings (not shown) in the article template 402 may be coupled tovacuum lines that create vacuum channels in the enclosed spaces betweenthe mold components 404, 406, and outer surfaces of support sections414, 416. When the channels are evacuated, positive pressure exertedfrom inside the support sections 414, 416 may push their outer flexiblemembranes into the surrounding fiber layers 412, 420 to press themagainst inside surfaces of the article template 402. The evacuation ofthe channels also creates a pressure gradient for the flow of apre-polymerized composition through the fiber layers.

Following the addition of the pre-polymerized composition with the fiberlayers, the combination may be heat cured to polymerize the polymerprecursors and form the fiber reinforced composite article. The heatingmay be done by a heat transfer system 422, 424, such as heatingfilaments integrated into the first and second mold components 404, 406.

Once the composite article has sufficiently cured, the mold components404, 406 may be separated and the fiber-reinforced composite windturbine blade removed from the article template 402.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the fiber” includesreference to one or more fibers and equivalents thereof known to thoseskilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A method of making a fiber-reinforced composite article, the methodcomprising: providing fibers to an article template, wherein the fibershave been treated with a sizing composition comprising a polymerizationcompound; providing a pre-polymerized composition to the articletemplate; adjusting a combination of the treated fibers andpre-polymerized composition to a polymerization temperature where thepre-polymerized composition polymerizes into a plastic around the fibersto form the fiber-reinforced composite article.
 2. The method of claim1, wherein the plastic comprises a thermoplastic.
 3. The method of claim1, wherein the polymerization compound comprises an initiator compoundor a catalyst.
 4. The method of claim 3, wherein the sizing compositioncomprises both an initiator compound and a catalyst.
 5. The method ofclaim 1, wherein the sizing composition further comprises acoupling-initiator compound.
 6. The method of claim 1, wherein thesizing composition further comprises a film-forming agent.
 7. The methodof claim 1, wherein the pre-polymerized composition comprises one ormore lactam monomers and the plastic comprises a polyamide.
 8. Themethod of claim 7, wherein the lactam monomers comprise one or morecaprolactams.
 9. The method of claim 7, wherein the polymerizationcompound includes an initiator compound having the formula:

wherein m is a integer with a value of 0 to
 12. 10. The method of claim7, wherein the polymerization compound includes an initiator compoundhaving a formula:R—X—(I)_(n) wherein n is an integer with a value of 1 to 5; R comprisesa terminal moiety selected from the group consisting of a hydrogen and ahydrocarbyl group; X comprises a linking moiety that links the R moietywith the one or more I moieties; and (I), comprises one or morepolymerization initiator moieties, wherein each of the initiatormoieties is capable of initiating a polymerization of the one or morelactam monomers, and wherein each of the initiator moieties is the sameor different.
 11. The method of claim 10, wherein the value of theinteger n is 1 to
 3. 12. The method of claim 10, wherein the linkingmoiety X comprises a covalent bond, an alkyl group, an aryl group, analkene group, or an amine group.
 13. The method of claim 10, wherein thelinking moiety X comprises—(CH₂)_(m)—, wherein m is a integer with avalue of 0 to
 12. 14. The method of claim 10, wherein the linking moietyX comprises —(H)N—(CH₂)_(m)—N(H)—, wherein m is a integer with a valueof 0 to
 12. 15. The method of claim 10, wherein at least one of thepolymer initiator moieties (I) comprises an organo-cyclic ring havingthe formula:

wherein

 represents a C₃ to C₁₂ substituted or unsubstituted cyclic hydrocarbonchain.
 16. The method of claim 15, wherein at least one of the initiatormoieties (I), has the formula:


17. The method of claim 7, wherein the polymerization compound includesa catalyst comprising a salt of a lactam, wherein the salt is an alkalimetal salt or an alkali-earth metal salt.
 18. The method of claim 17,wherein the catalyst comprises magnesium bromide caprolactam.
 19. Themethod of claim 7, wherein the pre-polymerized composition furthercomprises an initiator compound or a catalyst.
 20. The method of claim1, wherein the pre-polymerized composition comprises one or moremacrocyclic polyester oligomers, and the plastic comprises a polyester.21. The method of claim 20, wherein the macrocyclic polyester oligomerscomprise a polybutylene terephthalate.
 22. The method of claim 21,wherein the polybutylene terephthalate comprises cyclicpoly(1,4-butylene terephthalate).
 23. The method of claim 20, whereinthe polymerization compound comprises a catalyst selected from the groupconsisting of a tin-containing compound or a titanium-containingcompound.
 24. The method of claim 1, wherein the fibers provided to thearticle template further comprise a coating of the pre-polymerizedcomposition.
 25. A method of making a fiber reinforced compositearticle, the method comprising: treating fibers with a sizingcomposition comprising a polymerization compound; introducing thetreated fibers to a pre-polymerized composition; and adjusting acombination of the treated fibers and pre-polymerized composition to apolymerization temperature where the pre-polymerized compositionpolymerizes into a plastic around the fibers to form thefiber-reinforced composite article.
 26. The method of claim 25, whereinthe treated fibers and the pre-polymerized composition are introduced bya composite fabrication technique selected from the group consisting ofpultrusion, filament winding, reactive injection molding, structuralreactive injection molding, resin transfer molding, vacuum-assistedresin transfer molding, long fiber injection, sheet molding compound(SMC) molding, bulk molding compound (BMC) molding, a spray-upapplication, and a hand lay-up application.
 27. The method of claim 25,wherein the polymerization compound includes an initiator compoundhaving a formula:R—X—(I)_(n) wherein n is an integer with a value of 1 to 5; R comprisesa terminal moiety selected from the group consisting of a hydrogen and ahydrocarbyl group; X comprises a linking moiety that links the R moietywith the one or more I moieties; and (I)_(n) comprises one or morepolymerization initiator moieties, wherein each of the initiatormoieties is capable of initiating a polymerization of the one or morelactam monomers, and wherein each of the initiator moieties is the sameor different.
 28. The method of claim 25, wherein the pre-polymerizedcomposition comprises one or more lactam monomers and the plasticcomprises a polyamide.
 29. The method of claim 25, wherein thepre-polymerized composition comprises one or more macrocyclic polyesteroligomers, and the plastic comprises a polyester.
 30. The method ofclaim 25, wherein the polymerization compound comprises a firstinitiator precursor, and the pre-polymerized composition comprises atleast one polymerizable precursor and a second initiator precursor, andwherein following the introduction of the treated fibers to thepre-polymerized composition the first and second initiator precursorsreact to form an initiator capable of initiating the polymerization ofthe polymerizable precursor into the plastic at the polymerizationtemperature.
 31. The method of claim 30, wherein the first initiatorprecursor comprises ethyl benzoate and the second initiator precursorcomprises sodium caprolactam.
 32. A treated fiber that promotes apolymerization reaction to form a fiber-reinforced composite article,the treated fiber having at least one treated surface comprising apolymerization compound, wherein the polymerization compound initiatesor catalyzes the polymerization of a pre-polymerized composition. 33.The treated fiber of claim 32, wherein the polymerization compoundcomprises an initiator compound or a catalyst.
 34. The treated fiber ofclaim 33, wherein the initiator compound or the catalyst is notcovalently bonded to the treated surface of the fiber.
 35. The treatedfiber of claim 32, wherein the polymerization compound comprises acoupling-initiator compound covalently bonded to the treated surface ofthe fiber.
 36. The treated fiber of claim 32, wherein thepre-polymerized mixture comprises a lactam monomer or a macrocyclicpolyester oligomer.
 37. The treated fiber of claim 32, wherein thepolymerization compound initiates or catalyzes the polymerization of apre-polymerized composition into a thermoplastic polymer.
 38. Thetreated fiber of claim 32, wherein the treated fiber comprises a glassfiber.
 39. The treated fiber of claim 32, wherein the treated fiber ispart of a fiber mat.
 40. A fiber-reinforced composite articlecomprising: a plastic polymer matrix; and treated fibers bonded to theplastic polymer matrix by a first polymerization compound comprising areacted coupling-initiator compound with a reacted coupling moietycovalently bonded to the treated fiber, and a reacted initiator moietythat participated in the polymerization of the plastic polymer matrix;and a reacted second polymerization compound that also participated inthe polymerization of the plastic polymer without being covalentlybonded to the treated fiber.
 41. The article of claim 40, wherein theplastic polymer matrix is a thermoplastic polymer matrix.
 42. Thearticle of claim 40, wherein the reacted second polymerization compoundwas non-covalently coupled to at least a portion of the treated fibersprior to the polymerization of the plastic polymer.
 43. The article ofclaim 40, wherein the plastic polymer matrix comprises a polyamidepolymer or a polyester polymer.
 44. The article of claim 40, wherein thereacted second polymerization compound comprises an initiator compoundor a catalyst.